Method of manufacturing a two component sealing gasket for plastic pipe

ABSTRACT

A pipe sealing gasket is shown which is designed to be received within a raceway provided within the female, belled end of a section of plastic pipe which is assembled with a mating male pipe end to form a plastic pipe joint. The gasket is a two-component gasket having a softer, elastomeric portion and a harder, plastic ring portion. A splicing technique is used to form the softer, elastomeric portion with the harder, plastic portion being injection molded over the previously formed elastomeric portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Divisional of U.S. patent application Ser.No. 17/712,383, filed Apr. 4, 2022, which claims priority from U. S.Provisional Patent Application Ser. No. 63/201,186, filed Apr. 16, 2021,with the same title and by the same inventors.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to sealing gaskets and sealingsystems used for pipe joints in plastic pipelines in which a male spigotpipe section is installed within a mating female socket pipe section toform a pipe joint and to a method for manufacturing such a gasket.

Description of the Prior Art

Fluid sealing systems for plastic, fluid conveying pipes are used in avariety of industries. The pipes used in such systems are typicallyformed from thermoplastic materials including polyolefins and PVC. Informing a joint between sections of pipe, the spigot or male pipe end isinserted within the female or socket pipe end. An annular, elastomericring or gasket is typically seated within a groove formed in the socketend of the thermoplastic pipe. As the spigot is inserted within thesocket, the gasket provides the major seal capacity for the joint.Various types of sealing technologies have been employed to assure thesealing integrity of the pipe joint. It is important that the sealinggasket not be dislodged during the joint make up and that the gasket notbecome twisted or otherwise compromised in field applications.

Earlier gasketed sealing systems are known in which a homogeneous rubbergasket was generally deformable, allowing it to be flexed or bent byhand, accepting inverse curvature, and inserted within a mating internalraceway formed in the female, belled pipe end. The raceway in the femalepipe bell end was pre-formed, for example, using a collapsible mandrelbelling tool at the pipe manufacturing facility. A prior art attempt toinsure the integrity of such pipe joints involved the use of a pipegasket having a first distinct body region formed of an elasticallyyieldable sealing material, such as rubber, bonded to a second distinctbody region formed of a more rigid material, such as a rigid plastic.The intent was that the rigid body region of the gasket would assist inholding the gasket in place within the pipe groove. Other approaches tothe problem included the use of a homogeneous rubber ring with astiffening band which was inserted into a mating groove provided on theinternal diameter of the rubber ring.

In the early 1970's, a new technology was developed by Rieber & Son ofBergen, Norway, referred to in the industry as the “Rieber Joint.” TheRieber system employed a combined mould element and sealing ring forsealing a joint between the socket end and spigot end of two cooperatingpipes formed from thermoplastic materials. In the Rieber process, anelastomeric gasket was installed within an internal groove in the socketend of the female pipe as the female or belled end was simultaneouslybeing formed. Rather than utilizing a preformed groove, the Rieberprocess provided a prestressed and anchored elastomeric gasket duringthe belling operation. Because the gasket was installed simultaneouslywith the formation of the belled pipe end, a rigid, embedded reinforcingring could be supplied as a part of the gasket. Because the pipe groovewas, in a sense, formed around the gasket with its embedded reinforcingring, the gasket was securely retained in position and did not tend totwist or flip or otherwise allow impurities to enter the sealing zonesof the joint, thus increasing the reliability of the joint anddecreasing the risk of leaks or possible failure due to abrasion. TheRieber process is described in the following issued United Statespatents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872;3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.

Despite the advances offered by the Rieber process, the bellingoperation was somewhat complicated and costly. Also, certain situationsexist in which it would be desirable to manually install a gasket in thefield or at the manufacturing plant, or to remove one gasket andreinstall another within a preformed raceway in the selected pipe end,rather than utilizing an integrally installed gasket in which the groovein the pipe is formed around the gasket. So, in some instances, it maybe desirable to have a gasket which can be installed by hand by simplybending and installing the gasket in the pipe raceway.

The principles of materials science, as applied to gaskets of the abovetype have also advanced significantly in recent years. Two componentgaskets which feature a rubber-like section and a relatively harderplastic-type section have been developed in recent years which featureimproved materials for the different sections. For instance, PP/TPV,PP/TPE and PP/EPEM gaskets have been manufactured in the past. Eventhought such designs are known in the pipe sealing arts, there continuesto exist a need for improved manufacturing processes and designs formanufacturing such gaskets.

Accordingly, one object of the present invention is to provide animproved gasket which is securely retained within a preformed pipegroove without the necessity of a separate retaining band.

Another object of the invention is to provide such a sealing gasket withattributes which allow it to seal under low pressure or non-pressureconditions without being twisted or extruded, or displaced during fieldassembly, and yet which can be installed by hand in the bell raceway ofa plastic pipe.

Another object of the invention is to provide an improved manufacturingprocess for such a two-component gasket which process produces such agasket at less cost and with fewer steps than those involved in certainof the presently known manufacturing processes.

SUMMARY OF THE INVENTION

Although the manufacturing techniques shown herein might be used with avariety of different styles of sealing gaskets for plastic pipe, thediscussion which follows will be centered around a design especiallysuited for low pressure and non-pressure applications such asunderground drainage and sewer lines. The preferred gaskets of theinvention include a ring shaped, hard plastic band made, for example, ofa suitable polyolefin, e.g., polypropylene (PP). The hard plastic bandis joined to a separate region of rubber, synthetic rubber orthermoplastic elastomer (i.e., EPDM or TPV) which forms the primarysealing region for the gasket.

A unique manufacturing process is used to produce the gaskets of theinvention. In the first step in the manufacturing method, a gasketsection is extruded of a relatively softer rubber-like material to forma given length of material having opposing free ends and having adesired final profile cross section. Next, the opposing free ends of thegasket section are spliced together to form a continuous gasket band ofthe rubber-like material. The spliced gasket band is then placed in aconventional plastic injection mold and thereafter, a relatively harderplastic-like material is injected over the spliced gasket band in themold. Under the influence of heat and pressure, the harder plastic-likematerial bonds to the relatively softer rubber-like gasket band to forma finished two-component sealing gasket.

The splicing step can be accomplished by using a conventional splicingadhesive to join the free ends of the gasket section. Preferably, thesplicing step is accomplished by using using a hot PE or PP film that isplaced between the two opposing free ends of the gasket section andholding the free ends together until they cool and form a strong bondtherebetween. The opposing free ends of the gasket section can beheated, for example, by a heat source selected from the group consistingof a heating oven, a hot air gun, and an IR heater.

An improved pipe sealing gasket is also shown which is designed forreceipt within a raceway provided within a female bell socket end of athermoplastic pipe, the female bell socket end having a given internaldiameter which is designed to receive a given outer diameter of a matingmale thermoplastic pipe end to form a pipe joint. The improved gasket isformed with a a hard plastic ring shaped band having a leading noseregion and a trailing region. The trailing region is bonded to arelatively softer elastomer ring of rubber-like material which has anouter circumferential surface which forms a seal with the racewayprovided in the female bell socket and an inner circumferential surfacewhich forms a seal with the male thermoplastic pipe end.

The hard plastic band supports the elastomer ring, providing adequatestiffness to develop contact pressure between the outer circumferentialsurface of the elastomer ring and the raceway of the bell socket end ofthe pipe and between the inner circumferential surface and the matingmale pipe end.

The preferred sealing gasket is formed by the following steps:

-   -   extruding a gasket section of a relatively softer rubber-like        material to form a given length of material having opposing free        ends and having a desired final profile cross section;    -   splicing the opposing free ends of the gasket section together        to form a continuous gasket band of the rubber-like material;    -   placing the spliced gasket band in a conventional plastic        injection mold;    -   injecting a relatively harder plastic-like material over the        spliced gasket band in the mold and allowing the harder        plastic-like material to bond to the relatively softer        rubber-like gasket band to form a finished two-part sealing        gasket.

In one preferred form the gasket of the invention, both the elastomerouter circumferential surface and the inner circumferential surfaces ofthe elastomeric ring portion of the gasket form exposed circumferentialsealing surfaces, both of which are provided with a series ofcircumferential lands and grooves for engaging the female pipe socketend and the mating male pipe as the pipe joint is made up.

Additional objects, features and advantages will be apparent in thewritten description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an extruded rubber portion of gasket ofthe invention prior to splicing the ends thereof;

FIG. 2 is another view of the extruded rubber portion of the gasket ofthe invention, showing the free end portions;

FIG. 3 is a perspective view of the extruded rubber portion of FIGS. 1and 2 after splicing the free ends together;

FIG. 4 shows the first step in the manufacturing process used to formthe gasket of the invention in which the spliced extruded rubber portionof the gasket is placed into one section of a plastic injection mold;

FIG. 5 shows the extruded rubber portion in place in the mold section;

FIG. 6 is a view of the next step in the process in which the secondhalf of the mold is moved into position and closed and prior toinjecting the hard plastic material over the rubber portion of thegasket;

FIG. 7 is a view similar to FIG. 6 , but showing the next step in theprocess in which the hard plastic portion of the gasket has beeninjected over the softer, rubber portion;

FIGS. 8 and 9 show the next steps in the process of the invention inwhich the mold halves are separated and the completed gasket is removedfrom the mold;

FIG. 10 is a perspective view of the completed gasket of the invention;

FIG. 11 is a cross sectional view of the gasket of FIG. 10 ;

FIG. 12 is a partial sectional view of an end of a section of plasticpipe showing the bell end and raceway, with a gasket of the invention inplace in the raceway, the male pipe section being in position forinsertion into the bell.

FIG. 13 is a perspective view illustrating the stackable nature of thegaskets of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention described herein and the various features and advantageousdetails thereof are explained more fully with reference to thenon-limiting examples which are illustrated in the accompanying drawingsand detailed in the following description. Descriptions of well-knowncomponents and processes and manufacturing techniques are omitted so asto not unnecessarily obscure the workings of the invention. The examplesused herein are intended merely to facilitate an understanding of waysin which the invention herein may be practiced and to further enablethose of skill in the art to practice the invention. Accordingly, theexamples should not be construed as limiting the scope of the claimedinvention.

With reference first to FIGS. 10-12 , there is shown a pipe sealinggasket 11 which embodies the advantageous features of the invention.Although the method of the invention might be used to produce a varietyof styles of sealing gaskets for pipelines, the description whichfollows will make primary reference to a gasket designed in accordancewith the EN-1401-1 standard for PVC-U pipe and particularly to a gasketdesigned for low pressure or non-pressure applications for thewaterworks/municipal markets using a combination of materials to form atwo-component gasket.

FIG. 12 shows the gasket 11 installed within a raceway 13 providedwithin the belled end 15 of a female pipe section of thermoplastic pipe17. The female pipe section 17 can be formed of any of a variety ofcommercially available thermoplastic materials, such as the polyolefinfamily including polyethylene and polypropylene as well as polyvinylchloride and similar materials, most typically PVC. Thermoplastic pipesof this general type are used in a variety of industrial settingsincluding water, sewage and chemical industries. The belled end 15 ofthe thermoplastic pipe section has a mouth opening 19 which isengageable with a spigot end 23 of a mating male pipe section 25 to forma pipe joint. The gasket receiving raceway 13, in this case, has beenpre-formed in the pipe mouth opening 19 at the pipe manufacturingfacility. The gasket of the invention is flexible enough to be handinstalled in the raceway 13, or by using automated installationequipment.

FIG. 11 is a cross sectional view of the gasket 11, which gasket can beproduced by the method of the invention. The gasket 11 can be seen to bean annular, ring-shaped member having a main gasket body (27 in FIG. 10). As seen in the cross sectional view of FIG. 11 , the main body 27includes a first portion 29 formed of a flexible elastomeric material,such as a suitable natural or synthetic rubber. The elastomeric materialused to form the body portion 29 of the gasket will vary in compositiondepending upon the end application but may encompass a number ofdifferent natural and synthetic rubbers including, for example, styrenebutadiene rubber (SBR), ethylene propylene diene rubber (EPDM),acrylonitrile-butadiene rubber (NBR), nitrile rubber, etc. One preferredsynthetic material is EPDM rubber.

With reference again to FIG. 11 , the elastomeric portion 29 includes anouter sealing surface 31 which, in this case, is provided with a seriesof ribs or serrations 33. The surface 31 forms a seal with the racewayprovided in the belled end of the female pipe section (see FIG. 12 ).The elastomeric portion of the gasket body also includes a lower,primary sealing surface 35 which is also provided with ribs 37. As willbe understood by those skilled in the relevant arts, the primary sealingsurface 35 is a downwardly sloping face of the gasket body which forms acombination lip and compression seal region for the gasket. The lipregion is separated from the outer sealing surface 31 by a V-shapedrecess (shown generally as 39 in FIG. 11 ). The V-shaped recess allowsthe lip region of the gasket body to bend inwardly as the mating male,spigot end of a mating pipe section encounters the primary sealingsurface 35 of the gasket.

As is further evident from FIG. 11 , the elastomeric portion 29 of thegasket is reinforced by a relatively harder, plastic band region 41. Theband 41 is a continuous circumferential ring. The gasket body can thusbe thought of as a two-component gasket having a rubber element and ashaving a hard plastic element, the hard plastic element serving as thereinforcing element for the rubber portion of the gasket body. In use,the hard plastic region 41 both supports the elastomeric ring portionand provides adequate stiffness to develop contact pressure between theouter gasket body and the raceway (13 in FIG. 12 ) of the bell socketend of the pipe.

As can be seen in FIG. 12 , the hard plastic band region 41, togetherwith the supported outer elastomer ring portion 29 form a V-shapedprofile in cross section, the V-shape itself acting to promote aself-energizing behavior when hydrostatic pressure is applied to thepipe joint. In the particular example of the gasket shown in FIG. 12 ,both the elastomer outer ring portion 31 and the inner portion 35 of thegasket have exposed circumferential sealing surfaces which, aspreviously described, are provided with a series of circumferentiallands and grooves (e.g., lands 33, 37) for engaging the raceway in thefemale pipe socket end and the mating male pipe, respectively, as thepipe joint is made up. The particular shape and cross sectional profileof the gaskets facilitate stacking of the individual gaskets forshipping or storage (see FIG. 13 ).

As was previously mentioned, the rubber portions of the gaskets of theinvention can be formed of a rubber, such as for example, athermoplastic elastomer such as a thermoplastic vulcanizate, or a moretraditional rubber material such as a styrene butadiene rubber, ethylenepropylene diene monomer rubber or nitrile rubber. EPDM rubber is onepreferred material. The durometer of the rubber may vary depending onthe end application but will typically be in the range from about 40-70Shore A hardness, preferably about 40-60 Shore A. The hard plastic band41, on the other hand, is formed of a synthetic plastic material havinga durometer which is greater than the durometer of the rubber portionsof the gasket. The synthetic plastic material used for the band 41 ispreferably a material which shows an appropriate stiffness for theapplication at hand while allowing flexing during installation.

Although EPDM is a preferred material for the elastomeric portion of thegasket, other candidate materials for the rubber portion of the gasketinclude such materials as the “Thermoplastic Vulcanizates”, referred toas TPV's. These materials are part of the thermoplastic elastomer (TPE)family of polymers. However, these materials have the characteristic ofbeing closest in elastomeric properties to EPDM thermoset rubber,combining the characteristics of vulcanized rubber with the processingproperties of thermoplastics.

Various hard plastic type materials may be suitable candidates for useas the hard plastic band portion of the gasket. These materials includesuch materials as the polyolefins, such as polypropylene, as well asother materials such as polyvinylchloride and various “engineeredplastics.” The preferred material for the instant application is asuitable polypropylene (PP). The preferred sealing gaskets are thus aPP-EPDM composite.

The sealing gasket design of the invention, which has been described, isonly achieved by certain unique techniques used in the moldingoperation. As has been briefly discussed, there are variouscomplications or limitations which are inherent in the prior art moldingtechniques which are overcome by the manufacturing method of theinvention.

The improved manufacturing method of the invention will now be describedwith reference primarily to FIGS. 1-9 . The manufacturing technique usesa “splicing” step as a way to conveniently form the rubber portion ofthe sealing gasket. In the first step in the manufacturing method, agasket section of the relatively softer rubber-like material (EPDM) isextruded to form a given length of material (43 in FIG. 1 ) havingopposing free ends 45, 47, and having a desired final profile crosssection. FIG. 2 shows the free ends 47, 45, prior to the splicingoperation.

FIG. 3 shows the free ends of the rubber-like portion 43 of the gaskethaving been spliced together to form a continuous gasket band of therubber-like material. The splicing step can be accomplished in a numberof ways. For example, the splicing step can be accomplished by using aconventional splicing adhesive to join the free ends of the gasketsection. In one preferred method, the splicing step is accomplished byusing using a hot PE or PP film that is placed between the two opposingfree ends 45, 47, of the gasket section 43 and holding the free endstogether until they cool and form a strong bond therebetween. Theopposing ends 45, 47, can be heated by a heat source selected from thegroup consisting of a heating oven, a hot air gun, and an IR heater.

In the next step in the method, the EPDM ring 43 is placed in a plasticinjection mold. FIG. 4 shows the band 43 being placed in the lower onehalf 49 of an injection molding die of the type that will be familiar tothose skilled in the relevant arts. The mating upper half 51 of the moldis raised for ease of illustration. As can be seen in FIG. 4 , the lowermold half 49 has a first mold face 53 with a circumferential recess 55.As shown in FIG. 5 , in the next step of the manufacturing process, theEPDM band 43 is placed within the circumferential recess 55.

The second mold half 51 has a mold face which is essentially a mirrorimage of the first mold face. The first and second mold faces are thenunited and the relatively harder plastic material is injected over thespliced gasket band 43 in the mold and allowing the harder plastic-likematerial to bond to the relatively softer rubber-like gasket band toform a finished two-part sealing gasket. FIG. 7 shows the plasticportion 29 injected over the EPDM portion 43. The heat and pressure inthe mold cures the rubber sealing areas and adheres them to the hardplastic band portion. In FIG. 8 , the upper mold half 51 is beingseparated from the lower half 49. FIG. 9 shows the completed gasket 11being removed from the lower mold half 49.

A pipe sealing gasket is thus produced which is designed for receiptwithin a raceway provided within a female bell socket end of athermoplastic pipe, the female bell socket end having a given internaldiameter which is designed to receive a given outer diameter of a matingmale thermoplastic pipe end to form a pipe joint. The improved gasket ofthe invention is made up of a hard plastic ring shaped band having aleading nose region and a trailing region, the trailing region beingbonded to a relatively softer elastomer ring of rubber-like materialwhich has an outer circumferential surface which forms a seal with theraceway provided in the female bell socket and an inner circumferentialsurface which forms a seal with the male thermoplastic pipe end, as hasbeen described previously. The hard plastic band supports the elastomerring, providing adequate stiffness to develop contact pressure betweenthe outer circumferential surface of the elastomer ring and the racewayof the bell socket end of the pipe and between the inner circumferentialsurface and the mating male pipe end, and wherein the gasket is formedby the following steps:

-   -   extruding a gasket section of a relatively softer rubber-like        material to form a given length of material having opposing free        ends and having a desired final profile cross section;    -   splicing the opposing free ends of the gasket section together        to form a continuous gasket band of the rubber-like material;    -   placing the spliced gasket band in a conventional plastic        injection mold;    -   injecting a relatively harder plastic-like material over the        spliced gasket band in the mold and allowing the harder        plastic-like material to bond to the relatively softer        rubber-like gasket band to form a finished two-part sealing        gasket.

Both the elastomer outer circumferential surface and the innercircumferential surfaces of the elastomeric ring portion of the gasketform exposed circumferential sealing surfaces, both of which areprovided with a series of circumferential lands and grooves for engagingthe female pipe socket end and the mating male pipe as the pipe joint ismade up.

During the initial installation process of the sealing gasket within theraceway of the female pipe end, the gasket is bent and forced to conformto the annular groove. The rigid plastic portion of the gasket forcesthe gasket radially outward against the pipe as the male pipe end isinserted into the female belled pipe end. Due to its resiliency, theconformed exterior surface exerts pressure on the annular groove thuskeeping the gasket securely in place. The presence of the relativelyhard plastic band helps to firmly seat the gasket and to insure that thegasket body will not be blown out of the annular groove in use in thefield. When internal pressure or external forces act on the pipe joint,the gasket reacts dynamically by absorbing the internal or external loadand in turn exerts more pressure on the pipe joint to preserve theintegrity of the seal.

An invention has been provided with several advantages. The sealinggaskets of the invention are ideally suited for low pressure ornon-pressure sealing operations due to the lightweight and minimalisticaspects of the design. A two-component gasket is produced using a simplesplicing technique which is simple and economical to implement. Themethod used is actually backwards from usual two-component gasketmanufacturing techniques in which the softer, rubber portion of thegasket is injected over the previously formed hard plastic ring. In theresulting gaskets of the invention, the relatively softer rubber-likeportion of the gasket forms the primary sealing surfaces of the gasket.The relatively harder, plastic-like material forms a continuous ringwhich resists any tensile forces which would tend to separate thespliced gasket band portion of the finished gasket. The PP portion ofthe band supports the rubber sealing surfaces and provides most of thenecessary stiffness to develop adequate contact pressure against thesealing surfaces of the pipe joint (the bell raceway and the exterior ofthe mating male spigot). The V-type seal shape of the gasket promotesself-energizing behavior when hydrostatic pressure is applied to theresulting pipe joint.

While the invention has been shown in only one of its forms, it is notthus limited but is susceptible to various changes and modificationswithout departing from the spirit thereof.

1: A method of manufacturing a pipe sealing gasket designed for receipt within a raceway provided within a female bell socket end of a thermoplastic pipe, the method comprising the steps of: extruding a gasket section of a relatively softer rubber-like material to form a given length of material having opposing free ends and having a desired final profile cross section; splicing the opposing free ends of the gasket section together to form a continuous gasket band of the rubber-like material; placing the spliced gasket band in a conventional plastic injection mold; injecting a relatively harder plastic-like material over the spliced gasket band in the mold and allowing the harder plastic-like material to bond to the relatively softer rubber-like gasket band to form a finished two-part sealing gasket. 2: The method of claim 1, wherein the relatively softer, rubber-like material is selected from the group consisting of natural and synthetic rubbers. 3: The method of claim 2, wherein the relatively softer, rubber-like material is selected from the group consisting of EPDM, TPV and other TPE materials. 4: The method of claim 1, wherein the relatively harder, plastic-like material is a polyolefin. 5: The method of claim 4, wherein the relatively harder, plastic-like material is polypropylene. 6: The method of claim 1, wherein the splicing step is accomplished by using a conventional splicing adhesive to join the free ends of the gasket section. 7: A method of manufacturing a pipe sealing gasket designed for receipt within a raceway provided within a female bell socket end of a thermoplastic pipe, the method comprising the steps of: extruding a gasket section of a relatively softer rubber-like material to form a given length of material having opposing free ends and having a desired final profile cross section; splicing the opposing free ends of the gasket section together to form a continuous gasket band of the rubber-like material, the splicing being accomplished by using a hot PE or PP film that is placed between the two opposing free ends of the gasket section and holding the free ends together until they cool and form a strong bond therebetween; placing the spliced gasket band in a conventional plastic injection mold; injecting a relatively harder plastic-like material over the spliced gasket band in the mold and allowing the harder plastic-like material to bond to the relatively softer rubber-like gasket band to form a finished two-part sealing gasket, the relatively harder, plastic-like material forming a continuous ring which resists any tensile forces which would tend to separate the spliced gasket band portion of the finished gasket. 8: The method of claim 7, wherein the opposing free ends of the gasket section are heated by a heat source selected from the group consisting of a heating oven, a hot air gun, and an IR heater. 9: The method of claim 7, wherein the relatively softer, rubber-like material is selected from the group consisting of EPDM, TPV and other TPE materials. 10: The method of claim 7, wherein the relatively harder, plastic-like material is a polyolefin. 11: The method of claim 10, wherein the relatively harder, plastic-like material is polypropylene. 12-16. (canceled) 